Bumpers of vehicles are designed to absorb energy and/or transfer energy during vehicle impacts. Such vehicle impacts may include frontal and rear impacts. Impacts may occur with objects of varying size and mass, and various testing simulates such impacts. For example, one test is for low-speed damageability, which is simulated by impact tests that measure the amount of damage to the exterior of the bumper resulting from low-speed impacts. In these tests, little or no exterior damage to the bumper is desired to reduce the likelihood of costly repairs resulting from low-speed impacts. As another example, the vehicle may impact narrower, lighter objects, such as pedestrians. These impacts may be simulated by pedestrian protection (PedPro) impact tests.
These different classes of impacts present competing design factors for the bumper. During low-speed damageability tests, it may be beneficial for the bumper to be rigid, with no deformation, to reduce the likelihood of damage to the exterior of the bumper. In contrast, during an impact with a narrower object that may be a pedestrian, it may be more beneficial to reduce the stiffness of the bumper during deformation, which may reduce injuries to the pedestrian.